The invention pertains to a circuit arrangement for interfacing a television receiver to a home computer.
More specifically, the present invention relates to an interface circuit in a color-television receiver for providing the connection between the color-television receiver and a home computer which delivers at least one-bit digital color character signals whose minimum pulse duration is only approximately equal to the period of the clock signal. The invention is particularly applicable to a television receiver which reproduces a video signal containing interlaced fields after analog-to-digital conversion by means of a sampling signal, after digital signal processing in a digital circuit system controlled by the sampling signal or one of the harmonics thereof, which is used as a clock signal, and after digital-to analog conversion at twice the horizontal frequency.
In color-television using interlaced scanning, which permit the video signal to be reproduced line by line at twice the horizontal frequency, the analog video signal is processed digitally after analog-to-digital conversion and then converted back into analog form before being fed to the picture tube. As the digital video signal is written into a line memory at the horizontal frequency and read from this memory at twice the horizontal frequency, better flicker-free performance is obtained than with color-television receivers which do not reproduce the video signal at twice the horizontal frequency.
Conventional color-television receivers can be used to reproduce character signals delivered by a home computer. To do this, it is customary to bypass the subcircuits required for television reception and to feed the character signals, accompanied by horizontal and vertical synchronizing signals, to the picture tube.
This simple method of reproducing home-computer character signals is not readily applicable to the above-described color-television receivers with digital signal-processing circuitry etc., because the clock-signal system of the home computer and that of the color-television receiver are not frequency- and phase-synchronized.